\subsection{Shizhong's comment}
Castin has a paper about narrow resonance in some Fermi school 2007(8?)
\begin{quotation}
[12:02:51 AM] Shizhong Zhang: theoretical atomic physics (about the Feshbach resonance)
[12:03:03 AM] Shizhong Zhang: fredrich
\end{quotationn}

Two-body BEC end.  energy not not zero.  4.A.15 $E\neq0$. (likely gives effective  range)